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In compiler theory, a reaching definition for a given instruction is an earlier instruction whose target variable can reach (be assigned to) the given one without an intervening assignment. For example, in the following code: d1 : y := 3 d2 : x := y d1 is a reaching definition for d2. In the following, example, however:
In compiler theory, upwards exposed uses or reachable uses [1] are all uses of a variable that are reachable from a point in the program. A use of variable is a point or statement where that variable is referenced (read) but not changed.
A counterpart of a UD Chain is a definition-use chain (or DU chain), which consists of a definition D of a variable and all the uses U reachable from that definition without any other intervening definitions. [3] Both UD and DU chains are created by using a form of static code analysis known as data flow analysis.
In computer science, instruction selection is the stage of a compiler backend that transforms its middle-level intermediate representation (IR) into a low-level IR. In a typical compiler, instruction selection precedes both instruction scheduling and register allocation; hence its output IR has an infinite set of pseudo-registers (often known as temporaries) and may still be – and typically ...
In compiler theory, copy propagation is the process of replacing the occurrences of targets of direct assignments with their values. [1] A direct assignment is an instruction of the form x = y, which simply assigns the value of y to x. From the following code: y = x z = 3 + y Copy propagation would yield: z = 3 + x
In compiler theory, common subexpression elimination (CSE) is a compiler optimization that searches for instances of identical expressions (i.e., they all evaluate to the same value), and analyzes whether it is worthwhile replacing them with a single variable holding the computed value. [1]
For example, if all reaching definitions for the operands of some simple expression are outside of the loop, the expression can be moved out of the loop. Recent work by Moyen, Rubiano and Seiller uses data-flow dependence analysis [ 1 ] to detect not only invariant commands but larger code fragments such as an inner loop.
In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a type of intermediate representation (IR) where each variable is assigned exactly once. SSA is used in most high-quality optimizing compilers for imperative languages, including LLVM , the GNU Compiler Collection , and many commercial compilers.